New Zealand experiences hundreds of aftershocks, some with the intensity of 6.1, well into the morning on Monday.

Policemen and locals look at damage following an earthquake, along State Highway One near the town of Ward, south of Blenheim on New Zealand's South Island, November 14, 2016.REUTERS/Anthony Phelps

A 7.8 magnitude earthquake shook New Zealand shortly after midnight, killing at least two people and raising a tsunami warning that sent people scurrying to higher ground.

The tremor struck 16km underground near Hanmer Springs, some 91 km northeast of Christchurch in the South Island, and was felt across the country. The earthquake was of a greater magnitude than the devastating tremors that struck Christchurch in 2010 and 2011.

Buildings, roads and bridges collapsed in the quake and power lines and telecommunications were down in several parts of the country. The central business districts will remain paralyzed on Monday as the train network was closed for checks.

While the US Geological Survey put the intensity of Monday's quake at 7.8, New Zealand's Geonet said the quake's intensity was 7.5.

New Zealand experienced hundreds of aftershocks, some with the intensity of 6.1 magnitude, well into the morning on Monday.

Though the tsunami warning was later downgraded, people were still asked to stay away from beaches and rivers. Shortly after the midnight quake, residents of the capital woke up to tsunami warnings blaring on streets. People along the east coast sought higher ground.

"It was the most significant shock I can remember in Wellington ... There will be quite major costs around roads and infrastructure," Prime Minister John Key told reporters in the morning.

The Christchurch earthquake in 2011 had killed 185 people. New Zealand sits precariously on the seismically active "Ring of Fire", which witnesses around 90 percent of the world's earthquakes.

Prime Minister Key cancelled a trip to Argentina, and Australian Prime Minister Malcomlm Turnbull offered New Zealand all support.

"The situation is still unfolding and we don't yet know the full extent of the damage," Key said.